1. Field of the Invention
The present invention relates to a resin-sealed type semiconductor device in which a semiconductor chip and a part of a lead frame are sealed with a resin, and especially to a one-side sealed type semiconductor device in which a surface of a lead frame on which a semiconductor chip is mounted is sealed with a resin.
2. Description of Related Art
Resin-sealed type semiconductor devices in which a semiconductor chip and a part of a lead frame are sealed with a resin are widely used. Recently, as thin-type apparatus have come into general use, semiconductor devices mounted on these apparatus have also been requested to be thin-type. In conventional resin-sealed type semiconductor devices, generally both of the upper and lower portions of a semiconductor chip and a lead frame in the vicinity thereof are sealed with a resin. However, so-called one-side sealed type semiconductor devices have been developed which are made thin by sealing mainly the upper surface (the surface on which a semiconductor chip is mounted) of a lead frame.
FIG. 7 is a schematic sectional view showing the structure of a conventional one-side sealed type semiconductor device 50.
This semiconductor device 50 comprises a lead frame 51 having a supporting portion 52 and lead terminal portions 53, a semiconductor chip 54 mounted on the supporting portion 52, metal wires 55 for electrically connecting electrodes formed on the upper surface 54a of the semiconductor chip 54 and the upper surfaces 53a of the lead terminal portions 53 respectively, and a sealing resin 56 for sealing the semiconductor chip 54, metal wires 55, and a part of the upper surface of the lead frame 51.
The lead frame 51 has such a structure that the supporting portion 52 is disposed in the central portion thereof, and the lead terminal portions 53 are surrounding the supporting portion 52. The metal wire 55 is electrically connected to the upper surface 53a of the lead terminal portion 53. The lower surface 52b of the supporting portion 52 and the lower surfaces 53b of the lead terminal portions 53 are not coated with the sealing resin 56 but are exposed.
However, in s semiconductor device 50 having such a structure, moisture contained in the atmosphere and the like penetrates into the semiconductor device 50 from a boundary surface between the lead terminal portion 53 and the sealing resin 56 exposed at the bottom surface of the semiconductor device 50. The moisture having penetrated into the semiconductor device 50 travels upwardly along the boundary surface. The moisture having penetrated from below the connecting portion between the lead terminal portion 53 and the metal wire 55 reaches the connecting portion between the lead terminal portion 53 and the metal wire 55. Further, such moisture travels between the metal wire 55 and the sealing resin 56 and reaches an Al pad, which is the electrode formed on the upper surface 54a of the semiconductor chip 54. It has been a problem to be solved that such moisture, containing ions such as Cl−, Fe+ and Ni+, causes corrosion through chemical reaction with Al and has a harmful influence on the semiconductor device.